Spinal fusion is a surgical procedure used to correct problems with vertebrae of the spine. Spinal fusion fuses together the painful vertebrae so that they heal into a single, solid bone. In one method, the intervertebral disc between two vertebrae is removed and a small interbody spacer, also known as a cage, is inserted between the vertebrae. These interbody spacers usually contain bone graft material to promote bone healing and facilitate the fusion. After the interbody spacer is inserted, surgeons often use metal screws, plates, and rods to further stabilize the spine. Two common spinal fusion procedures are posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (TLIF). The type of interbody spacer is dependent on the type of fusion procedure being performed.